IMPORTANT: The actual implementation of the feature lies entirely in the hands of the content provider and totally *beyond* the perimeter of influence of this extension!

The »Prefer:« header has not been adopted by any standards organization yet, but is described in an IETF draft. It is currently e.g. supported[1] by later versions of Firefox, which activates the feature behind the scenes in colaboration with the operating system's parental control settings.